Aqueous tetrafluoroethylene polymer dispersion,process for producing the same, tetrafluoroethylene polymer powder,and molded tetrafluoroethylene polymer

ABSTRACT

The present invention provides a tetrafluoroethylene polymer aqueous dispersion obtained by carrying out a TFE polymerization in an aqueous medium in the presence of a fluorovinyl group-containing emulsifier, wherein the TFE polymer aqueous dispersion contains a particle comprising a TFE polymer dispersed in the aqueous medium, the fluorovinyl group-containing emulsifier comprises a fluorovinyl group-containing compound, and the TFE polymer aqueous dispersion has a fluorine-containing surfactant content of not higher than 1000 ppm by mass.

TECHNICAL FIELD

This invention relates to an aqueous tetrafluoroethylene [TFE] polymerdispersion, a method of producing the same, a TFE polymer powder, and aTFE polymer molding.

BACKGROUND ART

Patent Document 1 (Japanese Patent Publication (Kokoku) S61-33848)describes a method for producing an aqueous dispersion containingvinylidene fluoride [VdF]/TFE/hexafluoropropylene-basedfluorine-containing elastomer particles with a particle diameter of 0.02μm as dispersed therein which comprises carrying out the polymerizationreaction in the presence of a fluorine-based surfactant having apolymerizable double bond represented by the formulaCF₂═CFO(CF₂)_(n)COOM (in which n is an integer of 1 to 7 and M is anamine or alkali metal). However, there is no description about anaqueous dispersion containing a polymer having a high TFE monomer unitcontent.

Patent Document 2 (Japanese Kokai Publication H08-67795) describes amethod for producing an aqueous dispersion containing VdF-based polymerparticles with a particle diameter of not greater than 200 nm asdispersed therein at a concentration of not lower than 30% by mass whichmethod comprises carrying out the polymerization reaction in thepresence of at least one of various fluorine-containing surfactantshaving polymerizable double bonds. However, there is no descriptionabout an aqueous dispersion containing a polymer having a high TFEmonomer unit content or about the fluorine-containing surfactant contentin the aqueous VdF-based polymer dispersion obtained.

Patent Document 3 (Japanese Kokai Publication S60-250009), PatentDocument 4 (Japanese Kokai Publication S62-288614) and Patent Document 5(Japanese Kokai Publication S62-288616) respectively describe copolymersderived from a monomer represented by. CF₂═CFO(CF₃)SO₂F and TFE,copolymers derived from a monomer represented byCF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F and TFE, and copolymer derived from amonomer represented by CF₂═CFOCF₂(CF₃)OCF₂CF₂SO₂F and TFE. In each case,the polymerization is carried out in the presence of a relatively largeamount of a fluorine-based surfactant and, further, there is nodescription referring to the fact that a stable aqueous dispersioncontaining a particle comprising a TFE polymer very small in diameter isobtained.

DISCLOSURE OF INVENTION Problems which the Invention is to Solve

In view of the above-discussed state of the art, it is an object of theinvention to provide a high-concentration stable TFE polymer aqueousdispersion in spite of the fact that the polymerization is carried outin the absence or at a low concentration of a fluorine-containingsurfactant.

The present invention provides a tetrafluoroethylene polymer aqueousdispersion obtained by carrying out a tetrafluoroethylene polymerizationin an aqueous medium in the presence of a fluorovinyl group-containingemulsifier, wherein the tetrafluoroethylene polymer aqueous dispersioncontains a particle comprising a tetrafluoroethylene polymer dispersedin the aqueous medium,

the fluorovinyl group-containing emulsifier comprises a fluorovinylgroup-containing compound (I) represented by the general formula (I):CF₂═CF—(CF₂)_(a)—Y  (I)wherein a represents an integer of 1 to 10 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal,a fluorovinyl group-containing compound (II) represented by the generalformula (II):CF₂═CF— (CF₂C(CF₃) F)_(b)—Y  (II)wherein b represents an integer of 1 to 5 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal,

a fluorovinyl group-containing compound (III) represented by the generalformula (III):CF₂═CFO—(CFX)_(c)—Y  (III)wherein X represents F or —CF₃, c represents an integer of 1 to 10 and Yrepresents —SO₃M or —COOM in which M represents H, NH₄ or an alkalimetal, a fluorovinyl group-containing compound (IV) represented by thegeneral formula (IV):CF₂═CFO—(CF₂CFXO)_(d)—(CF₂)_(e)—Y  (IV)wherein X represents F or —CF₃, d represents an integer of 1 to 10, erepresents an integer of 1 to 3 and Y represents —SO₃M or —COOM in whichM represents H, NH₄ or an alkali metal, a fluorovinyl group-containingcompound (V) represented by the general formula (V):CH₂═CFCF₂O—(CF(CF₃)CF₂O)_(f)—CF(CF₃)—Y  (V)wherein f represents an integer of 0 to 10 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal, and/ora fluorovinyl group-containing compound (VI) represented by the generalformula (VI):CF₂═CFCF₂O—(CF(CF₃)CF₂O)_(g)—CF(CF₃)—Y  (VI)wherein g represents an integer of 1 to 10 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal,the tetrafluoroethylene polymer aqueous dispersion has afluorine-containing surfactant content of not higher than 1000 ppm bymass.

The present invention also provides a tetrafluoroethylene polymer powderwhich is obtained by coagulating the tetrafluoroethylene polymer aqueousdispersion.

The present invention further provides a tetrafluoroethylene polymermolding which is obtained by molding/processing using thetetrafluoroethylene polymer aqueous dispersion or thetetrafluoroethylene polymer powder.

The present invention provides a method of producing atetrafluoroethylene polymer aqueous dispersion by carrying out atetrafluoroethylene polymerization in an aqueous medium in the presenceof a fluorovinyl group-containing emulsifier, wherein thetetrafluoroethylene polymer aqueous dispersion contains a particlecomprising a tetrafluoroethylene polymer dispersed in the aqueous mediumand has a fluorine-containing surfactant content of not higher than 1000ppm by mass,

the fluorovinyl group-containing emulsifier is added in an amount of0.00001 to 2% by mass relative to the aqueous medium, and thefluorovinyl group-containing emulsifier comprises a fluorovinylgroup-containing compound (I) represented by the general formula (I):CF₂═CF—(CF₂)_(a)—Y  (I)wherein a represents an integer of 1 to 10 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal,a fluorovinyl group-containing compound (II) represented by the generalformula (II):CF₂═CF—(CF₂C(CF₃)F)_(b)—Y  (II)wherein b represents an integer of 1 to 5 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal,a fluorovinyl group-containing compound (III) represented by the generalformula (III):CF₂═CFO—(CFX)_(c)—Y  (III)wherein X represents F or —CF₃, c represents an integer of 1 to 10 and Yrepresents —SO₃M or —COOM in which M represents H, NH₄ or an alkalimetal, a fluorovinyl group-containing compound (IV) represented by thegeneral formula (IV):CF₂═CFO—(CF₂CFXO)_(d)—(CF₂)_(e)—Y  (IV)wherein X represents F or —CF₃, d represents an integer of 1 to 10, erepresents an integer of 1 to 3 and Y represents —SO₃M or —COOM in whichM represents H, NH₄ or an alkali metal, a fluorovinyl group-containingcompound (V) represented by the general formula (V):CH₂═CFCF₂O—(CF(CF₃)CF₂O)_(f)—CF(CF₃)—Y  (V)wherein f represents an integer of 0 to 10 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal, and/ora fluorovinyl group-containing compound (VI) represented by the generalformula (VI):CF₂═CFCF₂O—(CF(CF₃)CF₂O)_(g)—CF(CF₃)—Y  (VI)wherein g represents an integer of 1 to 10 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal.

In the following, the present invention is described in detail.

The TFE polymer aqueous dispersion of the invention is obtained bycarrying out a TFE polymerization in an aqueous medium in the presenceof a fluorovinyl group-containing emulsifier.

The fluorovinyl group-containing emulsifier comprises a fluorovinylgroup-containing compound (I), a fluorovinyl group-containing compound(II), a fluorovinyl group-containing compound (III), a fluorovinylgroup-containing compound (IV), a fluorovinyl group-containing compound(V) and/or a fluorovinyl group-containing compound (VI).

The fluorovinyl group-containing compound (I) is represented by thegeneral formula (I):CF₂═CF—(CF₂)_(a)—Y  (I)wherein a represents an integer of 1 to 10 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal.

In the above general formula (I), the integer a is preferably notgreater than 5, more preferably not greater than 2. The group Y ispreferably —COOM since such can make it easy to attain proper solubilityin water and surface activity, and M is preferably H or NH₄ since suchcan make it difficult for the compound (I) to remain in the TFE polymer.

The fluorovinyl group-containing compound (I) includes, among others,CF₂═CF—CF₂—COONH₄, CF₂═CF—CF₂COOH, CF₂═CF—CF₂CF₂—COOH, CF₂═CF—CF₂—COONa,CF₂═CF—CF₂—SO₃NH₄, CF₂═CF—CF₂SO₃H, CF₂═CF—CF₂CF₂—SO₃H andCF₂═CF—CF₂CF₂—SO₃Na. Among them, CF₂═CFCF₂—COONH₄ is preferred since astable aqueous dispersion of a TFE polymer relatively large in particlediameter can be readily obtained with the same.

The fluorovinyl group-containing compound (II) is represented by thegeneral formula (II):CF₂═CF—(CF₂C(CF₃)F)_(b)—Y  (II)wherein b represents an integer of 1 to 5 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal.

In the above general formula (II), b is preferably an integer notgreater than 3 from the surfactant activity viewpoint, and Y ispreferably —COOM since such can make it easy to attain proper solubilityin water and surface activity, and M is preferably H or NH₄ since suchcan make it difficult for the compound (II) to remain in the particlescomprising the TFE polymer.

The fluorovinyl group-containing compound (II) includes, for example,

and the like. Among them,

is preferred since the use thereof readily renders particles comprisingthe TFE polymer smaller in particle diameter.

The fluorovinyl group-containing compound (III) is represented by thegeneral formula (III):CF₂═CFO—(CFX)_(c)—Y  (III)wherein X represents F or —CF₃, c represents an integer of 1 to 10 and Yrepresents —SO₃M or —COOM in which M represents H, NH₄ or an alkalimetal.

In the above general formula (III), the moiety X is preferably —CF₃since adequate levels of solubility in water and surface activity can bereadily obtained in this case. The integer c is preferably an integernot greater than 5 from the solubility in water viewpoint, the moiety Yis preferably —COOM since such can make it easy to attain propersolubility in water and surface activity, and M is preferably H or NH₄since such can make it difficult for the compound (III) to remain in theparticles comprising the TFE polymer.

The fluorovinyl group-containing compound (III) includes, among others,CF₂═CF—OCF₂CF₂CF₂—COOH, CF₂═CF—OCF₂CF₂CF₂—COONa, CF₂═CF—OCF₂CF₂—COONH₄and CF₂═CF—OCF₂—COOH. Among them, CF₂═CF—OCF₂CF₂CF₂—COOH is preferredsince the use thereof readily renders particles comprising the TFEpolymer smaller in particle diameter.

The fluorovinyl group-containing compound (IV) is represented by thegeneral formula (IV):CF₂═CFO—(CF₂CFXO)_(d)—(CF₂)_(e)—Y  (IV)wherein X represents F or —CF₃, d represents an integer of 1 to 10, erepresents an integer of 1 to 3 and Y represents —SO₃M or —COOM in whichM represents H, NH₄ or an alkali metal.

In the above general formula (IV), the moiety X is preferably —CF₃ fromthe surfactant activity viewpoint, the integer d is preferably aninteger not greater than 5 from the solubility in water viewpoint, themoiety Y is preferably —COOM since such can make it easy to attainproper solubility in water and surface activity, the integer e ispreferably not greater than 2, and M is preferably H or NH₄.

The fluorovinyl group-containing compound (IV) includes, for example,CF₂═CF—O—CF₂CF(CF₃)—OCF₂CF₂—COOH,CF₂═CF—O—CF₂CF(CF₃)—OCF₂CF₂—COONH₄CF₂═CF—O—CF₂CF(CF₃)—OCF₂CF₂SO₃HCF₂═CF—O—CF₂CF(CF₃)—OCF₂CF₂SO₃NH₄and the like. Among them,CF₂═CF—O—CF₂CF(CF₃)—OCF₂CF₂—COOHCF₂═CF—O—CF₂CF(CF₃)—OCF₂CF₂—SO₃Hare preferred since the use thereof readily renders particles comprisingthe TFE polymer smaller in particle diameter.

The fluorovinyl group-containing compound (V) is represented by thegeneral formula (V):CH₂═CFCF₂O—(CF(CF₃) CF₂O)_(f)—CF(CF₃)—Y  (V)wherein f represents an integer of 0 to 10 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal.

In the above general formula (V), the integer f is preferably an integerof 0 to 5 from the surfactant activity viewpoint, and Y is preferably—COOM since such makes it easy to attain proper solubility in water andsurface activity, and M is preferably Na or NH₄ since such can make itdifficult for the compound (V) to remain in the particles comprising theTFE polymer.

The fluorovinyl group-containing compound (V) includes, for example,

and the like. Among them, CH₂═CFCF₂OCF(CF₃)—COONH₄ and/or CH₂═CFCF₂OCF(CF₃)—CF₂OCF (CF₃)—COONH₄ is preferred since the use thereof readilyrenders particles comprising the TFE polymer smaller in particlediameter and makes it difficult for itself to remain in the particlescomprising the TFE polymer.

The fluorovinyl group-containing compound (VI) is represented by thegeneral formula (VI):CF₂═CFCF₂O—(CF(CF₃)CF₂O)_(g)—CF(CF₃)—Y  (VI)wherein g represents an integer of 1 to 10 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal.

In the above general formula (VI), the integer g is preferably aninteger not greater than 3 from the surfactant activity viewpoint, andthe moiety Y is preferably —COOM since such makes it easy to attainproper solubility in water and surface activity. The moiety M ispreferably H or NH₄ since such makes it difficult for the compound (VI)to remain in the particles comprising the TFE polymer.

The fluorovinyl group-containing compound (VI) includes, for example,

and the like. Among these, the following are preferred since the usethereof readily renders particles comprising the TFE polymer smaller inparticle diameter:

From the viewpoint that particles comprising the TFE polymer smaller inparticle diameter can readily be obtained and a TFE polymer aqueousdispersion high in TFE polymer concentration can readily be obtained,the fluorovinyl group-containing emulsifier preferably comprises thefluorovinyl group-containing compound (I), fluorovinyl group-containingcompound (II), fluorovinyl group-containing compound (III), fluorovinylgroup-containing compound (IV) and/or fluorovinyl group-containingcompound (V) and, more preferably, it comprises the fluorovinylgroup-containing compound (II), fluorovinyl group-containing compound(III) and/or fluorovinyl group-containing compound (V).

From the viewpoint that particles comprising the TFE polymer smaller inparticle diameter can readily be obtained, the fluorovinylgroup-containing emulsifier still more preferably comprises afluorovinyl group-containing compound (i) represented by the generalformula (i):CF₂═CF—(O)_(h)—(CF₂CF(CF₃)O)_(i)—(CF₂)_(j)—Y  (i)wherein h represents an integer of 0 or 1, j represents an integer of 0to 2, j represents an integer of 1 to 3 and Y represents —SO₃M or —COOMin which M represents H, NH₄ or an alkali metal, and/or a fluorovinylgroup-containing compound (ii) represented by the general formula (ii):CH₂═CFCF₂O—(CF(CF₃)CF₂O)_(k)—CF(CF₃)—Y  (ii)wherein k represents an integer of 0 to 3 and Y represents —SO₃M or—COOM in which M represents H, NH₄ or an alkali metal.

In the above general formula (i), h is preferably 1, i is preferably 0or 1, j is preferably 1 or 2, and Y is preferably —SO₃Na or —COONH₄.

In the above general formula (ii), k is preferably 0 to 2 and Y ispreferably —COONH₄ or —COONa.

Use may be made, as the fluorovinyl group-containing emulsifier, one ortwo or more of the six genera mentioned above, namely the fluorovinylgroup-containing compound (I), fluorovinyl group-containing compound(II), fluorovinyl group-containing compound (III), fluorovinylgroup-containing compound (IV), fluorovinyl group-containing compound(V) and fluorovinyl group-containing compound (VI), and each of the sixfluorovinyl group-containing compound genera may comprise one or two ormore species.

The above-mentioned fluorovinyl group-containing compounds can beprepared in the conventional manner.

The TFE polymer aqueous dispersion of the invention is obtained bycarrying out the TFE polymerization in the presence of theabove-mentioned fluorovinyl group-containing emulsifier, so that the TFEpolymer concentration is high and the particles comprising the TFEpolymer are small in particle diameter. Therefore, the TFE polymeraqueous dispersion of the invention contains particles comprising theTFE polymer excellent in moldability/processability and in physicalproperties, for example mechanical stability.

In the TFE polymer aqueous dispersion of the invention, the “aqueousmedium” is the reaction medium for carrying out the polymerizationtherein and is a liquid containing water. The aqueous medium is notparticularly restricted but may be any one containing water. In additionto water, it may contain a fluorine-free organic solvent such as analcohol, ether, ketone or paraffin wax and/or a fluorine-containingorganic solvent such as C318.

The TFE polymer aqueous dispersion of the invention may be any oneobtained by carrying out the TFE polymerization in the above-mentionedaqueous medium in the presence of the above-mentioned fluorovinylgroup-containing emulsifier and, thus, it may be one obtained bycopolymerizing TFE and another monomer other than TFE.

The monomer other than TFE is not particularly restricted but may be,for example, another fluorine-containing monomer other than TFE or afluorine-free monomer.

The “fluorine-containing monomer” may be mentioned, for example, afluoroolefin, a fluorinated cyclic monomer or a fluorinated alkyl vinylether.

The fluoroolefin includes, among others, hexafluoropropylene [HFP],vinyl fluoride, vinylidene fluoride [VDF], trifluoroethylene,hexafluoroisobutylene and perfluorobutylethylene.

The fluorinated cyclic monomer includesperfluoro-2,2-dimethyl-1,3-dioxole [PDD] andperfluoro-2-methylene-4-methyl-1,3-dioxolane [PMD], among others.

The fluorinated alkyl vinyl ether includes, among others, onesrepresented by the formula CZ¹ ₂═CZ²OR¹ or CZ¹ ₂═CZ²OR²OR wherein thetwo Z¹s may be the same or different and each represents H or F, Z² is Hor F, R¹ is an alkyl group containing 1 to 8 carbon atoms with a part orall of the hydrogen atoms being substituted by fluorine atoms and R² isan alkylene group containing 1 to 8 carbon atoms with a part or all ofthe hydrogen atoms being substituted by fluorine atoms.

Preferred as the fluorinated alkyl vinyl ether are, for example,perfluoro(methyl vinyl ether) [PMVE], perfluoro(ethyl vinyl ether)[PEVE] and perfluoro(propyl vinyl ether) [PPVE].

The fluorine-free monomer mentioned above is not particularly restrictedbut may be any one copolymerizable with TFE, for example ahydrocarbon-based monomer. The hydrocarbon-based monomer may be onecontaining one or more of non-fluorine halogen atoms, oxygen, nitrogenand like elements and various substituents.

As the above hydrocarbon-based monomers, there may be mentioned, forexample, alkenes, alkyl vinyl ethers, vinyl esters, alkyl allyl ethers,and alkyl allyl esters.

The TFE polymer aqueous dispersion is generally obtained by carrying outthe polymerization by adding a polymerization initiator to theabove-mentioned fluorovinyl group-containing emulsifier, TFE and such anoptionally added monomer other than TFE as mentioned above. Usable asthe polymerization initiator are, for example, persulfate salts such asammonium persulfate [APS] and organic peroxides such as disuccinoylperoxide [DSP] and diglutaroyl peroxide, either singly or in the form ofa mixture thereof. The polymerization initiator may be used in the formof a redox system through combined use of a reducing agent such assodium sulfite. During polymerization, the radical concentration in thesystem may be adjusted by adding a radical scavenger such ashydroquinone or catechol or a peroxide decomposer such as ammoniumsulfite.

The TFE polymer aqueous dispersion of the invention may also be oneobtained by carrying out the polymerization using a fluorine-containingsurfactant other than the fluorovinyl group-containing emulsifiermentioned above (hereinafter, such surfactant is referred to as“non-byproduct fluorine-containing surfactant”), one or more of suchadditives known in the art as chain transfer agents and radicalscavengers in addition to the above-mentioned fluorovinylgroup-containing emulsifier, TFE and such an optional polymerizationinitiator and/or monomer other than TFE as mentioned above.

The term “non-byproduct fluorine-containing surfactant” as used hereinmeans a compound containing at least one fluorine atom in the molecularstructure thereof and having surfactant activity, which is to be addedon the occasion of the above-mentioned TFE polymerization. The“non-byproduct fluorine-containing surfactant” is conceptually differentfrom the short-chain byproduct fluorine-containing surfactant to bedescribed later herein as formed as a byproduct upon TFE polymerizationin that it is added on the occasion of TFE polymerization.

As the non-byproduct fluorine-containing surfactant, there may bementioned, for example, carboxylic acid compounds represented byZ³-(CH₂)_(n)—COOHwherein Z represents F or H and n represents an integer of 3 to 20, aswell as alkali metal salts, ammonium salts, amine salts and quaternaryammonium salts thereof;carboxylic acid compounds represented byZ⁴-(CF₂CF₂)_(m)—COOHwherein Z⁴ represents F or Cl and m represents an integer of 3 to 13, aswell as alkali metal salts, ammonium salts, amine salts and quaternaryammonium salts thereof; andcarboxylic acid compounds represented byRfO—(CF (CF₃)CF₂O)_(r)—CF (CF₃)—Z⁵wherein Rf represents a perfluoroalkyl group containing 1 to 7 carbonatoms, r represents an integer of 0 to 10 and Z⁵ represents —COOM or—SO₃M in which M represents H, NH₄ or an alkali metal.

In carrying out the TFE polymerization, one or two or more suchnon-byproduct fluorine-containing surfactant may be added.

The TFE polymer aqueous dispersion of the invention can be obtained byany of the polymerization methods known in the art provided that the TFEpolymerization is carried out in an aqueous medium in the presence ofthe above-mentioned fluorovinyl group-containing emulsifier.

The TFE polymerization is carried out generally after removal ofdissolved air by repetitions of nitrogen feeding under pressure anddegassing.

In the above-mentioned TFE polymerization, the fluorovinylgroup-containing surfactant is preferably added in an amount of 0.00001to 2% by mass relative to the aqueous medium.

When the level of addition of the fluorovinyl group-containingemulsifier is lower than 0.00001% by mass, the TFE polymer tends to formlarge particles insufficiently stable against settling. When it ishigher than 2% by mass, the polymerization reactivity may be reduced,rather leading to failure to produce the effects of the use of theabove-mentioned fluorovinyl group-containing surfactant in someinstances.

A more preferred lower limit to the level of addition of the fluorovinylgroup-containing emulsifier is 0.0001% by mass and a still morepreferred lower limit is 0.001% by mass. A more preferred upper limit tothe level of addition of the fluorovinyl group-containing surfactant is1% by mass and a still more preferred upper limit is 0.5% by mass.

In the above-mentioned TFE polymerization, the total level of additionof the whole monomer or monomer composition can be properly determinedaccording to the molecular weight and/or amount of the desired TFEpolymer to be produced.

From the economy and/or productivity viewpoint, the total level ofaddition of the whole monomer or monomer composition is preferably notlower than 10% by mass relative to the aqueous medium and, the reactionsystem stability viewpoint, it is preferably not higher than 150% bymass relative to the aqueous medium.

A more preferred lower limit to the total level of addition of the wholemonomer or monomer composition is 20% by mass relative to the aqueousmedium, and a more preferred upper limit is 100% by mass and a stillmore preferred upper limit is 70% by mass.

The level of addition of the other monomer than TFE among the wholemonomer composition can be adequately determined according to thecomposition of the desired TFE polymer.

In the TFE polymerization, TFE and the non-TFE monomer to be optionallyadded are generally fed either continuously or intermittently so thatthe pressure in the reaction system may be maintained within the rangedescribed later herein during the polymerization reaction.

The polymerization initiator mentioned above is preferably added in anamount of 0.005 to 1% by mass relative to the aqueous medium.

When the polymerization initiator is added in an amount smaller than0.005% by mass relative to the aqueous medium, the polymerization ratetends to become extremely slow and, when it is added in an amountexceeding 1% by mass relative to the aqueous medium, the electrolyteconcentration increases and the particles comprising the TFE polymertend to become greater in particle diameter.

A more preferred lower limit to the above addition level is 0.01% bymass, and a more preferred upper limit to the addition level is 0.5% bymass.

The above-mentioned non-byproduct fluorine-containing surfactant can beadded at levels that will not adversely affect the properties of the TFEpolymer aqueous dispersion of the invention. Generally, it can be addedat levels not exceeding 1% by mass relative to the aqueous medium.Preferably, the non-byproduct fluorine-containing surfactant is added atlevels not exceeding 0.5% by mass, still more preferably at levels notexceeding 0.2% by mass. However, the above-mentioned TFE polymerizationis preferably carried out in the absence of any non-byproductfluorine-containing surfactant since then it becomes easy to treat thewaste liquid possibly resulting from the TFE polymer aqueous dispersionobtained.

In the TFE polymerization, the addition of the fluorovinylgroup-containing emulsifier is preferably carried out in the manner of asupplementary addition with the progress of the TFE polymerizationreaction if need be.

When, in the TFE polymerization, the fluorovinyl group-containingemulsifier is carried out with such supplementary addition, thereactivity of TFE with the fluorovinyl group-containing compound isimproved, so that the content of the fluorovinyl group-containingemulsifier in the TFE polymer aqueous dispersion obtained can be reducedand the content of the fluorine-containing surfactant, which is to bedescribed later herein, can be reduced.

The above-mentioned supplementary addition may be continuous orintermittent. Thus, the emulsifier may be added before the start of theTFE polymerization reaction and then supplementally added continuouslyor intermittently, or the addition thereof may be started after thestart of the TFE polymerization with the progress of the polymerizationreaction, followed by continuous or intermittent supplementary addition,without addition thereof before the start of the polymerization reactionor at the initial stage of the polymerization reaction.

In the TFE polymerization, the addition of the non-byproductfluorine-containing surfactant, too, may be carried out in the manner ofthe supplementary addition with the progress of the TFE polymerizationreaction according to need, like the addition of the fluorovinylgroup-containing emulsifier.

In the TFE polymerization, the reaction conditions such as temperature,pressure and polymerization time can be properly selected according tothe amount of the TFE polymer aqueous dispersion to be prepared, thecomposition and concentration of the TFE polymer.

The TFE polymerization is generally carried out at a polymerizationtemperature of 10 to 100° C. and a polymerization pressure of 0.05 to 5MPaG for 5 to 100 hours.

The TFE polymer aqueous dispersion of the invention is one obtained bythe above-mentioned TFE polymerization and containing a particlecomprising a TFE polymer dispersed in the aqueous medium mentionedabove.

So long as it is one obtained by the above-mentioned TFE polymerization,the TFE polymer aqueous dispersion of the invention may be an aqueousdispersion as obtained just after the polymerization without carryingout such a procedure as dilution or concentration after theabove-mentioned TFE polymerization or may be an aqueous dispersionobtained by carrying out such a procedure.

So long as it is one obtained by polymerizing TFE in an aqueous mediumin the presence of the above-mentioned fluorovinyl group-containingemulsifier, the TFE polymer mentioned above is not particularlyrestricted but may be, for example, a TFE homopolymer or a modifiedpolytetrafluoroethylene [modified PTFE] or a TFE copolymer derived fromTFE and a monomer or monomers other than TFE.

Since the TFE polymer is obtained by carrying out the TFE polymerizationin an aqueous medium in the presence of the above-mentioned fluorovinylgroup-containing emulsifier, a part or parts of the polymer chainthereof may contain the above-mentioned fluorovinyl group-containingcompound as added thereto.

The term “modified PTFE” as used herein means a non-melt-processablecopolymer of TFE and a minor constituent monomer other than TFE.

The minor constituent monomer includes, among others, theabove-mentioned perfluoroolefins, fluorohaloolefins, fluoro(alkyl vinylether) species, fluorinated cyclic monomers, andperfluoroalkylethylenes.

The minor constituent monomer-derived minor constituent monomer unitcontent in the above modified PTFE is generally within the range of0.001 to 2 mole percent relative to all the monomer units.

The term “monomer unit”, such as the minor constituent monomer unitmentioned above, as used herein means a part of the molecular structureof the TFE polymer which is that part derived from the correspondingmonomer. Thus, for example, the TFE unit is a part of the molecularstructure of the TFE polymer and is the segment derived from TFE asrepresented by —(CF₂—CF₂)—. The term “all the monomer units” as usedhereinabove indicates all the monomer-derived segments occurring in themolecular structure of the TFE polymer.

The “monomer unit content relative to all the monomer units” is thevalue determined by subjecting the TFE polymer to molten-state NMRmeasurement.

The “minor constituent monomer unit content (mole percent) relative toall the monomer units” so referred to herein means the proportion (molepercent) of the minor constituent monomer from which the minorconstituent monomer unit is derived to the monomers from which “all themonomer units” mentioned above are derived, namely the total amount ofthe monomers constituting the TFE polymer.

The term “TFE copolymer” as used herein means a copolymer of TFE and atleast one monomer other than TFE, with the content of the monomer unitderived from the monomer other than TFE relative to all the monomerunits exceeding 2 mole percent.

In the above-mentioned TFE copolymer, the monomer other than TFE is notparticularly restricted but includes, among others, the above-mentionedfluorine-containing monomers and fluorine-free monomers.

The TFE copolymer may be, for example, a melt-processable fluoropolymer.

The melt-processable fluoropolymer preferably has a melt viscosity ofnot higher than 10⁹ Pa/s at 380° C.

The melt-processable fluoropolymer is, for example, a fluoropolymerconstituting a melt-processable fluororesin or an elastomericfluorine-containing copolymer.

The melt-processable fluororesin-constituting fluoropolymer includes,among others, ethylene/TFE copolymers [ETFEs], TFE/HFP copolymers [FEPs]and TFE/perfluoro(alkyl vinyl ether) copolymers [TFE/PFVE copolymers].

As the TFE/PFVE copolymers, there may be mentioned TFE/PMVE copolymers[MFAs], TFE/PEVE copolymers and TFE/PPVE copolymers [PFAs] and, amongthem, MFAs and PFAs are preferred, and PFAs are more preferred.

The above-mentioned elastomeric copolymer includes TFE/propylenecopolymers and HFP/ethylene/TFE copolymers, among others.

The TFE polymer mentioned above preferably has a TFE unit contentexceeding 40 mole percent relative to all the monomer units since thepolymer then becomes excellent in thermal stability and other physicalproperties and easy to handle.

The TFE polymer more preferably has a TFE unit content of 60 molepercent or higher, still more preferably 95 mole or higher, relative toall the monomer units.

The TFE polymer may be a non-perfluoro-based polymer other than theperfluoro-based polymer described later herein but preferably is aperfluoro-based polymer since such polymer is excellent in thermalstability and other physical properties and easy to handle.

The “perfluoro-based polymer” so referred to herein includes, within themeaning thereof, a perfluoropolymer obtained by polymerizing aperfluoromonomer(s) alone or a fluoropolymer obtained by using, as acomonomer, a non-perfluoro compound at usage levels at which thephysical properties of the above-mentioned perfluoropolymer will not bedeteriorated.

As the perfluoro-based polymer, there may be mentioned, for example,fluorine-free functional group- and/or C—H bond-containingfluoropolymers.

The perfluoro-based polymer preferably has a perfluoro unit content ofnot lower than 90 mole percent, more preferably not lower than 95 molepercent, still more preferably not lower than 98 mole percent, relativeto all the monomer units.

The perfluoro-based polymer mentioned above may contain any kind ofmonomer unit in addition to TFE so long as it comes under the definitiongiven above.

The TFE polymer is more preferably a perfluoro-based polymer having aTFE unit content exceeding 40 mole percent relative to all the monomerunits, still more preferably a perfluoro-based polymer having a TFE unitcontent exceeding 60 mole percent relative to all the monomer units,most preferably a perfluoro-based polymer having a TFE unit contentexceeding 95 mole percent relative to all the monomer units, since sucha polymer is excellent in thermal stability and other physicalproperties and easy to handle.

The TFE polymer in the TFE polymer aqueous dispersion of the inventiongenerally has a number average molecular weight of 100000 to 20000000. Apreferred lower limit to the average molecular weight of the TFE polymeris 500000 from the moldability/processability viewpoint, and a preferredupper limit is 10000000.

The average molecular weight of the TFE polymer, so referred to herein,is the value obtained based on the standard specific gravity (SSG)measured according to ASTM D 1457-69.

The particles comprising the TFE polymer in the TFE polymer aqueousdispersion of the invention preferably have an average primary particlediameter of 50 to 500 nm.

When the average primary particle diameter is smaller than 50 nm, anincrease in TFE polymer concentration tends to result in a rapidincrease in the viscosity of the TFE polymer aqueous dispersion and,when the average primary particle diameter is greater than 500 nm, thedispersion stability and mechanical stability, among others, of the TFEpolymer aqueous dispersion tend to decrease.

A preferred lower limit to the above-mentioned average primary particlediameter is 100 nm, and a more preferred lower limit is 150 nm. Apreferred upper limit to the average primary particle diameter is 400nm, and a more preferred upper limit is 350 nm.

The average primary particle diameter can be adjusted by selecting orspecifying the level of addition of the fluorovinyl group-containingemulsifier for use in the TFE polymerization, the supplementary additionof the fluorovinyl group-containing emulsifier, the polymerizationpressure, the minor constituent monomer species and the content thereofin the modified PTFE and so forth.

The term “average primary particle diameter” as used herein means theaverage primary particle diameter of the particles comprising the TFEpolymer in the TFE polymer aqueous dispersion as obtained afterpolymerization and not yet subjected to such a procedure as dilution orconcentration.

The average primary particle diameter is the value determined indirectlyusing a working curve showing the relation between the transmittance forincident light at 550 nm per unit length and the average particlediameter determined by electron photomicrography as constructed with aTFE polymer aqueous dispersion adjusted to a predetermined solid matterconcentration and measuring such transmittance of the TFE polymeraqueous dispersion which is the target of measurement.

The TFE polymer aqueous dispersion of the invention has afluorine-containing surfactant content of not higher than 1000 ppm basedon the mass of the TFE polymer aqueous dispersion.

The fluorine-containing surfactant concentration, so referred to herein,is measured by extracting, under refluxing, the aqueous dispersionobtained with such a solvent as methanol used as the extractant,fractionating the thus-recovered extract by column chromatography andcomparing the data obtained with the data for a standard aqueoussolution having a concentration of 1000 ppm.

The term “fluorine-containing surfactant” as used herein means the sumtotal of all surfactants that occur in the above-mentioned aqueousdispersion and have at least one fluorine atom in the molecularstructure thereof. As the fluorine-containing surfactant, there may bementioned, for example, (1) fluorovinyl group-containing emulsifiers,(2) short-chain byproduct fluorine-containing carboxylic acid compounds,(3) non-byproduct fluorine-containing surfactants, and (4) monomer-addedfluorovinyl group-containing emulsifiers.

The above-mentioned fluorine-containing surfactant content is preferablynot higher than 100 ppm, more preferably not higher than 50 ppm, stillmore preferably not higher than 30 ppm, based on the mass of the TFEpolymer aqueous dispersion since the waste liquid resulting from the TFEpolymer aqueous dispersion then becomes easy to treat.

Among the fluorine-containing surfactants enumerated above, thefluorovinyl group-containing emulsifiers (1) and non-byproductfluorine-containing surfactants (3) are those described hereinabove.

The short-chain byproduct fluorine-containing carboxylic acid compounds(2) include, within the meaning thereof, those short-chain carboxylicacid compounds derived from such a monomer as TFE and formed asbyproducts when a persulfate salt such as ammonium persulfate [APS] oran organic peroxide such as disuccinoyl peroxide [DSP] is used as apolymerization initiator in the above-mentioned TFE polymerization. Theshort-chain byproduct fluorine-containing carboxylic acid compounds hasa —COOH terminus formed upon addition of a persulfate-derived radical(.OSO₃M [M representing H, NH₄ or an alkali metal]) or an organicperoxide-derived radical (.OR³ [R³ representing an organic group]) to amonomer-based short chain terminus, followed by decomposition.

The short-chain byproduct fluorine-containing carboxylic acid compoundsare fluorine-containing compounds containing, as a hydrophobic group, anoligomer moiety derived from 1 to about 5 molecules of such a monomer asTFE and, as a hydrophilic group, the —COOH terminus and therefore act assurfactants. The rate of polymerization reaction is very rapid in theabove-mentioned TFE polymerization and the oligomer formation percentageis very low, so that the short-chain fluorine-containing carboxylic acidcompounds are scarcely formed. Therefore, the TFE polymer aqueousdispersion of the invention as obtained by TFE polymerization containssubstantially no short-chain byproduct fluorine-containing carboxylicacid compounds, so that the fluorine-containing surfactant contenttherein is low.

The monomer-added fluorovinyl group-containing emulsifiers (4) areformed as byproducts in the TFE polymerization mentioned above and arethose emulsifiers which comprise compounds resulting from addition ofoligomers composed of one to about 5 molecules of such a monomer as TFEto the above-mentioned fluorovinyl group-containing compound. The rateof polymerization reaction in the above-mentioned TFE polymerization isvery fast and the polymerization reaction progresses under incorporationof the above-mentioned fluorovinyl group-containing compound intopolymer chains. Therefore, the proportions of the unreacted monomer(s)and the above-mentioned oligomers occurring in the aqueous dispersionobtained are very small and the residual amount of the fluorovinylgroup-containing compound therein is very small, so that suchmonomer-added fluorovinyl group-containing emulsifiers are hardlyformed. Thus, the TFE polymer aqueous dispersion of the invention asobtained by the above-mentioned TFE polymerization is substantially freeof such monomer-added fluorovinyl group-containing emulsifiers and,accordingly, it is low in the content of the above-mentionedfluorine-containing surfactants.

Since the TFE polymer aqueous dispersion of the invention is obtained byTFE polymerization in the further presence of the above-mentionedfluorovinyl group-containing emulsifier, the TFE polymer generallycomprises molecules resulting from addition of the above-mentionedfluorovinyl group-containing compound to the molecular structurethereof.

Upon addition of the fluorovinyl group-containing compound to the TFEpolymer, the carboxylate group [—COO⁻] derived from the fluorovinylgroup-containing compound takes its position on the surface of particlecomprising the TFE polymer, so that the particles comprising the TFEpolymer themselves become improved in dispersion stability. Therefore,the TFE polymer aqueous dispersion of the invention can have gooddispersion stability even when the fluorine-containing surfactantcontent is not higher than 1000 ppm by mass relative to the aqueousmedium.

Even when it is just as obtained by the above-mentioned TFEpolymerization, the TFE polymer aqueous dispersion of the invention islow in fluorine-containing surfactant content and shows goodmoldability/processability. Preferably, however, the fluorine-containingsurfactant is removed by such a known purification method as phaseseparation or ion exchange treatment.

The solid matter concentration in the TFE polymer aqueous dispersion ofthe invention is generally 5 to 70% by mass. When the solid matterconcentration is higher than 70% by mass, the stability of the TFEpolymer aqueous dispersion itself tends to decrease. The solid matterconcentration can be properly adjusted by selecting the level ofaddition of the monomer TFE and/or the above-mentioned monomer(s) otherthan TFE.

Preferably, the TFE polymer aqueous dispersion of the invention has asolid matter concentration of 5 to 65% by mass.

A more preferred lower limit to the above solid matter concentration is10% by mass in view of the recovery rate in recovering the TFE polymerby coagulation or flocculation, and a more preferred lower limit is 20%by mass from the better purification efficiency viewpoint.

A more preferred upper limit to the above solid matter concentration is40% by mass in view of the possibility of the solid matter in the TFEpolymer aqueous dispersion in the vessel being prevented from adheringto the vessel wall.

The “solid matter concentration” so referred to herein is the valuedetermined based on the mass loss after drying the TFE polymer aqueousdispersion at 150° C. for 1 hour.

When one or more of such known compounding ingredients as pigments,thickening agents, dispersants, antifoaming agents, antifreezing agentsand film-forming auxiliaries are incorporated therein or one or morefurther other polymer compounds are compositely used therewith, the TFEpolymer aqueous dispersion of the invention can be used as a water-basedcoating paint.

As the use of the TFE polymer aqueous dispersion of the invention, theremay also be mentioned the use thereof in the form of a powder obtainedby subjecting the TFE polymer aqueous dispersion to coagulation orflocculation and drying the thus recovered solid matter, if desiredfollowed by granulation.

The TFE polymer powder obtained by coagulating the above-mentioned TFEpolymer aqueous dispersion also constitutes an aspect of the presentinvention.

The coagulation is generally effected by diluting the aqueous dispersionobtained by emulsion polymerization, for example a polymer latex, withwater to a polymer concentration of 10 to 20% by mass, optionallyadjusting the pH to neutrality or alkalinity, and stirring the dilutionin a vessel equipped with a stirrer more vigorously than during thereaction.

In the above coagulation, the stirring may also be carried out whileadding, as a coagulant, a water-soluble organic compound such asmethanol or acetone, or an inorganic salt such as potassium nitrate orammonium carbonate or an inorganic acid such as hydrochloric acid,sulfuric acid or nitric acid.

A pigment- and/or filler-containing TFE polymer fine powder with thepigment(s) and/or filler(s) homogeneously mixed therein can also beobtained by adding a pigment or pigments for coloration and/or one ormore of various fillers for improving mechanical characteristics beforeor during the above coagulation.

The coagulation may also be carried out continuously using in-linemixers, for instance.

The drying of the wet powder obtained by the above coagulation isgenerally carried out by such means as vacuum, high frequency or hot airwhile maintaining a state in which the wet powder is not caused to flowexcessively, preferably in a state of standing still.

When the TFE polymer occurs as a fine powder, friction among powderparticles, in particular at elevated temperatures, is generallyunfavorable since a weak shearing force can readily fibrillate theparticles comprising the TFE polymer; upon fibrillation, the particleslose their original stable particle structure.

The above-mentioned drying is carried out at a drying temperature of 10to 250° C., preferably 100 to 200° C.

The TFE polymer powder of the invention generally has an averageparticle diameter of 50 μm to 1000 μm. A preferred lower limit to theaverage particle diameter is 100 μm from the moldability/processabilityviewpoint, among others, and a preferred upper limit is 700 μm.

The “average particle diameter of the TFE polymer powder of theinvention”, so referred to herein, is the value measured by means of ascanning electron microscope.

The TFE polymer powder of the invention, which is obtained from the TFEpolymer aqueous dispersion of the invention, shows goodmoldability/processability and is useful as a raw material for producingTFE polymer moldings excellent in mechanical characteristics and otherphysical properties.

The TFE polymer powder of the invention, when it is a TFE polymer finepowder, is preferably used for molding purposes, in particular, andsuitable fields of application thereof include tubes and the like foruse in hydraulic systems and fuel systems in aircrafts, automobiles andthe like, flexible hoses for liquid chemicals, steam and the like, andelectric wire coverings, among others.

The TFE polymer moldings obtained by molding/processing using the TFEpolymer aqueous dispersion of the invention or the TFE polymer powder ofthe invention also constitutes an aspect of the present invention.

The TFE polymer moldings of the invention may be in the form of pellets,molded articles, coatings or cast films.

In the present specification, the production of the pellets, theproduction of the molded articles, the production of the coatings and/orthe production of the cast films is sometimes referred to“molding/processing”.

The above molding/processing can be properly carried out by one of themethods known in the art.

Among the molding/processing methods, the method of producing pellets isnot particularly restricted but may be, for example, the methodcomprising feeding the TFE polymer powder of the invention to a kneaderor extruder, followed by melting and kneading to produce pellets.

The method of producing molded articles is not particularly restrictedbut may include, among others, compression molding, extrusion molding,paste extrusion moldings, and injection molding.

The coating processing is generally carried out by applying theabove-mentioned TFE polymer aqueous dispersion to articles or substratesto be coated. The method of application in the coating processing is notparticularly restricted but includes, among others, spray coating, dipcoating, brush coating, and electrostatic coating.

In the above coating processing, a composition obtained by adding anonionic surfactant to the TFE polymer aqueous dispersion prior toapplication to thereby stabilize the TFE polymer aqueous dispersion,followed by further concentration and addition of an organic orinorganic filler(s) according to the intended use can be applied. Suchcomposition, when applied to metal or ceramic substrates, can give coatsurfaces having nonstickiness and a low coefficient of friction andexcellent in gloss, smoothness, wear resistance, weather resistance andthermal stability. It is thus suited for coating rolls, cooking utensilsand the like and for dip coating of glass cloths, among others.

As for the method of cast film formation, there may be mentioned, forexample, the method comprising applying the dispersion to a substrateand, after drying, peeling off the coat film from the substrate, ifdesired, by placing the coated substrate in water, for instance.

The molding/processing conditions can adequately selected according tothe method of molding/processing and the composition and amount of theTFE polymer to be subjected to molding/processing, among others.

The TFE polymer moldings of the invention, which are obtained from theTFE polymer aqueous dispersion of the invention or the TFE polymerpowder of the invention, are excellent in durability, weatherresistance, surface characteristics, mechanical characteristics andother physical properties.

The method of producing a TFE polymer aqueous dispersions according tothe invention comprises carrying out the TFE polymerization in anaqueous medium in the presence of a fluorovinyl group-containingemulsifier.

The fluorovinyl group-containing emulsifier, TFE and aqueous mediumspecies, addition levels and preferred ranges thereof to be used oremployed in the method of producing a TFE polymer aqueous dispersionaccording to the invention are the same as those described hereinabovereferring to the TFE polymer aqueous dispersion of the invention.

In carrying out the method of producing a TFE polymer aqueous dispersionaccording to the invention, the fluorovinyl group-containing emulsifieris added in an amount of 0.00001 to 2% by mass relative to the aqueousmedium.

In carrying out the method of producing a TFE polymer aqueous dispersionof the invention, it is also possible to use any of those monomers otherthan TFE and non-byproduct fluorovinyl group-containing surfactants andother materials mentioned hereinabove referring to the TFE polymeraqueous dispersion of the present invention.

However, the method of producing a TFE polymer aqueous dispersionaccording to the invention preferably comprises carrying out the TFEpolymerization in an aqueous medium in the absence of the non-byproductfluorine-containing surfactant since the treatment of the liquid wastepossibly coming from the TFE polymer aqueous dispersion obtained becomeseasy then.

In the method of producing a TFE polymer aqueous dispersion according tothe invention, the addition of the fluorovinyl group-containingemulsifier is preferably carried out in the manner of a supplementaryaddition with the progress of the TFE polymerization reaction.

When, in the method of producing a TFE polymer aqueous dispersionaccording to the invention, the addition of the fluorovinylgroup-containing emulsifier is carried out in the above-mentioned mannerof the supplementary addition, the reactivity between TFE and thefluorovinyl group-containing compound in the TFE polymerization becomesbetter, so that the TFE polymer aqueous dispersion obtained is low inthe content of the fluorovinyl group-containing emulsifier, namely thefluorine-containing surfactant mentioned above.

In the method of producing a TFE polymer aqueous dispersion according tothe invention, the above-mentioned supplementary addition can be carriedout in the same manner as described hereinabove referring to the TFEpolymer aqueous dispersion of the invention.

The TFE polymer aqueous dispersion obtained by the method of producing aTFE polymer aqueous dispersion according to the invention each containsa particle comprising a TFE polymer dispersed in the aqueous medium andthe content of the fluorine-containing surfactant therein is not higherthan 1000 ppm by mass.

The above-mentioned TFE polymer and particle comprising the TFE polymerin each of the TFE polymer aqueous dispersion obtained by the method ofproducing a TFE polymer aqueous dispersion according to the inventionare respectively the same as described hereinabove referring to the TFEpolymer aqueous dispersion of the invention.

The above-mentioned particle comprising the TFE polymer is the particleresulting from addition of the above-mentioned fluorovinylgroup-containing compound to the above-mentioned TFE polymer, and theymay have the fluorovinyl group-containing compound-derived carboxylategroups positioned on the particle surface. Such particle comprising theTFE polymer is itself excellent in dispersion stability and, therefore,the TFE polymer aqueous dispersion obtained by the method of producing aTFE polymer aqueous dispersion according to the invention is excellentin dispersion stability in spite of the fact that thefluorine-containing surfactant content is not higher than 1000 ppm bymass.

Effects of the Invention

The TFE polymer aqueous dispersion of the invention, which has theabove-mentioned constitution, is stable at a high solid matterconcentration and is generally excellent in moldability/processabilityand, therefore, it is useful as a raw material for producing a TFEpolymer powder or a TFE polymer molding. The TFE polymer aqueousdispersion of the invention is very low in fluorine-containingsurfactant content and is industrially useful since that factfacilitates the treatment of the liquid waste formed uponmolding/processing thereof, among others.

The TFE polymer powder of the invention and the TFE polymer molding ofthe invention are obtained from the TFE polymer aqueous dispersion ofthe invention and, therefore, the TFE polymer powder of the invention isexcellent in moldability/processability and the TFE polymer molding ofthe invention is excellent in mechanical characteristics and otherphysical properties.

The method of producing a TFE polymer aqueous dispersion according tothe invention, which has the constitution described above, can give TFEpolymer aqueous dispersions very low in fluorine-containing surfactantcontent and, therefore, is useful.

BEST MODES FOR CARRYING OUT THE INVENTION

The following examples are further illustrative of the presentinvention. These examples are, however, by no means limitative of thescope of the invention.

EXAMPLE 1 Preparation of the TFE Polymer Aqueous Dispersion

A 3-liter stainless steel autoclave equipped with a stirring impellerwas charged with 1.5 liters of deionized water, 60 g of paraffin wax(melting point 60° C.) and 700 mg of fluorovinyl group-containingcompound 1 [CF₂═CFOCF₂CF(CF₃)OCF₂CF₂CF₂SO₃Na], and the system inside waspurged with TFE. The inside temperature was raised to 70° C., and theautoclave was charged with TFE under pressure until arrival of theinside pressure at 0.78 MPa and further charged with 5 g of a 0.6% (bymass) aqueous solution of ammonium persulfate [APS] to initiate the TFEpolymerization reaction. Since otherwise the polymerization systeminside pressure would lower with the progress of the polymerization, thereaction was continued while the inside pressure was maintained at 0.78MPa by continuous additional feeding of TFE. At 6.5 hours after thestart of the polymerization, the remaining TFE was purged off and thepolymerization was discontinued. The aqueous dispersion obtained wassubjected to the following measurements (1) to (5).

(1) Solid matter concentration: The aqueous dispersion obtained wasdried at 150° C. for 1 hour and that concentration was calculated basedon the resulting loss in mass.

(2) Average primary particle diameter: The dispersion was diluted to asolid matter concentration of about 0.02% by mass, the transmittance forincident light at 550 nm per unit length was measured and that diameterwas indirectly determined based on a working curve constructed so as toshow the relation between such transmittance and the average particlediameter determined by electron photomicrography.

(3) AI (amorphous index): A 150-μm-thick film was prepared using a pressand subjected to IR absorbance measurement, and the ratio of theabsorbance at 778 cm⁻¹ to the absorbance at 2367 cm⁻¹ was calculated asthe AI value. The AI is an indicator of crystallinity, and a lower AIvalue is considered to indicate that the introduction of the fluorovinylgroup-containing compound is less influential.

(4) Standard specific gravity (SSG): The SSG was determined according toASTM D 1457-69.

(5) Fluorine-containing surfactant concentration: The aqueous dispersionobtained was dried at 50° C. for 1 hour, a 1-g portion of the solidmatter obtained was added to 50 g of methanol, extraction was carriedout under refluxing at the boiling point of methanol, the extractrecovered was fractionated by column chromatography (apparatus: TOSOHHPLC-8000, column ODS-120T 150 mm×4.6 mm φ, mobile phaseacetonitrile/0.05 mole percent phosphate buffer (pH 6)=6/4, flow rate 1ml/minute), and the concentration in question was determined bycomparison with the data obtained for a standard aqueous solution havinga fluorine-containing surfactant concentration of 1000 ppm and expressedin mass concentration.

EXAMPLES 2 TO 6 Preparation of TFE Polymer Aqueous Dispersions

TFE polymer aqueous dispersions were prepared in the same manner as inExample 1 except that the fluorovinyl group-containing compounds 2 to 6specified below (hereinafter, Compounds 2 to 6) were respectively usedin lieu of fluorovinyl group-containing compound 1. They were subjectedto the measurements (1) to (5).

Compound 2: CF₂═CFOCF₂CF₂CF₂—COONa

Compound 3: CH₂═CFCF₂O—(CF(CF₃) CF₂O)₂CF (CF₃)—COONH₄

Compound 4: CH₂═CF—CF₂OCF(CF₃)—CF₂OCF(CF₃)—COONH₄

Compound 5: CH₂═CF—CF₂OCF(CF₃)—COONH₄

Compound 6: CF₂═CF—CF₂CF₂—COONH₄

EXAMPLE 7 Preparation of a TFE Polymer Aqueous Dispersion

A TFE polymer aqueous dispersion was prepared in the same manner as inExample 4 except that 110 mg of Compound 4 was added prior topolymerization and five 110-mg portions thereof were further added athourly intervals during the polymerization reaction. The dispersion wassubjected to the measurements (1) to (5).

The measurement results in each example are shown in Table 1. TABLE 1Amount Average Fluorine- of primary containing compound PolymerizationSolid matter particle surfactant used time concentration diameterconcentration (mg) (hours) (mass %) (nm) AI value SSG (ppm) Example 1700 6.5 19.2 206 0.081 2.205 46 Example 2 470 7.0 14.4 175 0.143 2.23228 Example 3 908 3.7 13.3 182 0.068 2.218 25 Example 4 660 3.1 11.8 1800.074 2.238 18 Example 5 410 3.0 10.5 176 0.082 2.242 19 Example 6 2901.5 5.2 281 0.121 2.225 29 Example 7 660 5.7 25.6 200 0.079 2.222 7

As shown in Table 1, the TFE polymer aqueous dispersions obtained inExamples 1 to 7 were very low in fluorine-containing surfactantconcentration. In particular, the TFE polymer aqueous dispersionobtained in Example 7 was lower in fluorine-containing surfactantconcentration and higher in solid matter concentration than the TFEpolymer aqueous dispersion obtained in Example 4, revealing that thoseobtained by the supplementary addition of the fluorovinylgroup-containing compound are preferred as the TFE polymer aqueousdispersions of the invention.

INDUSTRIAL APPLICABILITY

The TFE polymer aqueous dispersion of the invention, which has theabove-mentioned constitution, is high in TFE polymer concentration, isstable and is generally excellent in moldability/processability as welland, therefore, it is useful in the production of a TFE polymer powderor TFE polymer moldings. The TFE polymer aqueous dispersion of theinvention is very low in fluorine-containing surfactant content and isuseful since that fact facilitates the treatment of the liquid wasteformed upon molding/processing of the TFE polymer aqueous dispersion,among others.

The TFE polymer powder of the invention and the TFE polymer moldings ofthe invention are obtained from the TFE polymer aqueous dispersion ofthe invention and, therefore, the TFE polymer powder of the invention isexcellent in moldability/processability and the TFE polymer moldings ofthe invention are excellent in mechanical characteristics and otherphysical properties.

The method of producing TFE polymer aqueous dispersion according to theinvention, which has the constitution described above, can give TFEpolymer aqueous dispersions very low in fluorine-containing surfactantcontent and, therefore, is useful.

1. A tetrafluoroethylene polymer aqueous dispersion obtained by carryingout a tetrafluoroethylene polymerization in an aqueous medium in thepresence of a fluorovinyl group-containing emulsifier, wherein saidtetrafluoroethylene polymer aqueous dispersion contains a particlecomprising a tetrafluoroethylene polymer dispersed in said aqueousmedium, said fluorovinyl group-containing emulsifier comprises afluorovinyl group-containing compound (I) represented by the generalformula (I):CF₂═CF—(CF₂)_(a)—Y  (I) wherein a represents an integer of 1 to 10 and Yrepresents —SO₃M or —COOM in which M represents H, NH₄ or an alkalimetal, a fluorovinyl group-containing compound (II) represented by thegeneral formula (II):CF₂═CF—(CF₂C(CF₃)F)_(b)—Y  (II) wherein b represents an integer of 1 to5 and Y represents —SO₃M or —COOM in which M represents H, NH₄ or analkali metal, a fluorovinyl group-containing compound (III) representedby the general formula (III):CF₂═CFO—(CFX)_(c)—Y  (III) wherein X represents F or —CF₃, c representsan integer of 1 to 10 and Y represents —SO₃M or —COOM in which Mrepresents H, NH₄ or an alkali metal, a fluorovinyl group-containingcompound (IV) represented by the general formula (IV):CF₂═CFO—(CF₂CFXO)_(d)—(CF₂)_(e)—Y  (IV) wherein X represents F or —CF₃,d represents an integer of 1 to 10, e represents an integer of 1 to 3and Y represents —SO₃M or —COOM in which M represents H, NH₄ or analkali metal, a fluorovinyl group-containing compound (V) represented bythe general formula (V):CH₂═CFCF₂O—(CF(CF₃)CF₂O)_(f)—CF(CF₃)—Y  (V) wherein f represents aninteger of 0 to 10 and Y represents —SO₃M or —COOM in which M representsH, NH₄ or an alkali metal, and/or a fluorovinyl group-containingcompound (VI) represented by the general formula (VI):CF₂═CFCF₂O—(CF(CF₃)CF₂O)_(g)—CF(CF₃)—Y  (VI) wherein g represents aninteger of 1 to 10 and Y represents —SO₃M or —COOM in which M representsH, NH₄ or an alkali metal, said tetrafluoroethylene polymer aqueousdispersion has a fluorine-containing surfactant content of not higherthan 1000 ppm by mass.
 2. The tetrafluoroethylene polymer aqueousdispersion according to claim 1, wherein the tetrafluoroethylene polymerhas a tetrafluoroethylene unit content exceeding 40 mole percent.
 3. Thetetrafluoroethylene polymer aqueous dispersion according to claim 1,wherein the tetrafluoroethylene polymer is a perfluoro-based polymer. 4.The tetrafluoroethylene polymer aqueous dispersion according to claim 1,wherein the tetrafluoroethylene polymerization is carried out in theabsence of any non-byproduct fluorine-containing surfactant.
 5. Thetetrafluoroethylene polymer aqueous dispersion according to claim 1,wherein the fluorovinyl group-containing emulsifier comprises thefluorovinyl group-containing compound (I), the fluorovinylgroup-containing compound (III), the fluorovinyl group-containingcompound (IV) and/or the fluorovinyl group-containing compound (V). 6.The tetrafluoroethylene polymer aqueous dispersion according to claim 5,wherein the fluorovinyl group-containing emulsifier comprises afluorovinyl group-containing compound (i) represented by the generalformula (i):CF₂═CF—(O)_(h)—(CF₂CF(CF₃)O)_(i)—(CF₂)_(j)—Y  (i) wherein h representsan integer of 0 or 1, i represents an integer of 0 to 2, j represents aninteger of 1 to 3 and Y represents —SO₃M or —COOM in which M representsH, NH₄ or an alkali metal, and/or a fluorovinyl group-containingcompound (ii) represented by the general formula (ii):CH₂═CFCF₂O—(CF(CF₃)CF₂O)_(k)—CF(CF₃)—Y  (ii) wherein k represents aninteger of 0 to 3 and Y represents —SO₃M or —COOM in which M representsH, NH₄ or an alkali metal.
 7. The tetrafluoroethylene polymer aqueousdispersion according to claim 1, which has a solid matter concentrationof 5 to 70% by mass.
 8. The tetrafluoroethylene polymer aqueousdispersion according to claim 1, wherein the particle comprising thetetrafluoroethylene polymer has an average primary particle diameter of50 to 500 nm.
 9. A tetrafluoroethylene polymer powder which is obtainedby coagulating the tetrafluoroethylene polymer aqueous dispersionaccording to claim
 1. 10. A tetrafluoroethylene polymer molding which isobtained by molding/processing using the tetrafluoroethylene polymeraqueous dispersion according to claim
 1. 11. A method of producing atetrafluoroethylene polymer aqueous dispersion by carrying out atetrafluoroethylene polymerization in an aqueous medium in the presenceof a fluorovinyl group-containing emulsifier, wherein saidtetrafluoroethylene polymer aqueous dispersion contains a particlecomprising a tetrafluoroethylene polymer dispersed in said aqueousmedium and has a fluorine-containing surfactant content of not higherthan 1000 ppm by mass, said fluorovinyl group-containing emulsifier isadded in an amount of 0.00001 to 2% by mass relative to said aqueousmedium, and said fluorovinyl group-containing emulsifier comprises afluorovinyl group-containing compound (I) represented by the generalformula (I):CF₂═CF—(CF₂)_(a)—Y  (I) wherein a represents an integer of 1 to 10 and Yrepresents —SO₃M or —COOM in which M represents H, NH₄ or an alkalimetal, a fluorovinyl group-containing compound (II) represented by thegeneral formula (II):CF₂═CF—(CF₂C(CF₃)F)_(b)—Y  (II) wherein b represents an integer of 1 to5 and Y represents —SO₃M or —COOM in which M represents H, NH₄ or analkali metal, a fluorovinyl group-containing compound (III) representedby the general formula (III):CF₂═CFO—(CFX)_(c)—Y  (III) wherein X represents F or —CF₃, c representsan integer of 1 to 10 and Y represents —SO₃M or —COOM in which Mrepresents H, NH₄ or an alkali metal, a fluorovinyl group-containingcompound (IV) represented by the general formula (IV):CF₂═CFO—(CF₂CFXO)_(d)—(CF₂)_(e)—Y  (IV) wherein X represents F or —CF₃,d represents an integer of 1 to 10, e represents an integer of 1 to 3and Y represents —SO₃M or —COOM in which M represents H, NH₄ or analkali metal, a fluorovinyl group-containing compound (V) represented bythe general formula (V):CH₂═CFCF₂O—(CF(CF₃)CF₂O)_(f)—CF(CF₃)—Y  (V) wherein f represents aninteger of 0 to 10 and Y represents —SO₃M or —COOM in which M representsH, NH₄ or an alkali metal, and/or a fluorovinyl group-containingcompound (VI) represented by the general formula (VI):CF₂═CFCF₂O—(CF(CF₃)CF₂O)_(g)—CF(CF₃)—Y  (VI) wherein g represents aninteger of 1 to 10 and Y represents —SO₃M or —COOM in which M representsH, NH₄ or an alkali metal.
 12. The method of producing atetrafluoroethylene polymer aqueous dispersion according to claim 11,wherein the addition of the fluorovinyl group-containing emulsifier iscarried out in the manner of a supplementary addition with the progressof a tetrafluoroethylene polymerization reaction.